Actually, the way to do mortal hiccup combat is to stretch your diaphragm (the breathing muscle between your chest and stomach) and sometimes your rib muscles. The reason why is that if any muscle of yours is spasming uncontrollably (which is the case with the hiccups because your breathing is irregular), it means that you need to stretch it.
(I experienced this once with my hand when shoveling gravel because I was using my wrist muscles a lot, but obviously you are using your breathing muscles all the time so they spasm more easily.)
To stretch your diaphragm (bottom belly muscle):
1. Take a breathe of air (does not have to be a deep breathe)
2. Tense your rib muscles to push the air down into your diaphagm. You should feel a slight pull down there, kind of like what happens when you stretch your arms or legs.
3. Exhale. Breathe normally.
To stretch your rib muscles:
1. Kneel down in standard crawling position.
2. Extend your arms all the way out so they are straight, and allow your forehead to touch the floor. (This is a lazy version of the downward dog yoga position; I don't approve of yoga philosophy, but you can use a physical position to cure your hiccups!)
3. Breathe normally. You should feel a pull against your chest. The idea is to use gravity to push against your rib muscles and stretch them out.
You may not want to do something like this every time you have the hiccups, but if you are in a situation where you need to get rid of them in short order, these methods will work for sure.
Finally, sometimes when doing this you might get a couple of hiccups that are from your throat muscles spasming. However, this is easily fixed by gently massaging the front of your throat, leaning your head back to stretch the front of your neck, or getting a drink of water.